The present invention relates to a method of and an equipment for optical inspection of strip and sheet products for the detection of surface defects, which method comprises
producing images of successive parts of the surface of a product,
converting the images produced to an analog signal on the basis of the brightness of pixels,
converting the analog signal to a digital signal by providing each pixel with a digital value representing its brightness,
analyzing the digital signal for the detection of surface defects on the product and
giving information of the surface defects detected.
A method of detecting surface defects on a moving strip, similar to the one described above, is known from U.S. Pat. No. 4,665 317. By means of such an equipment, it is possible to alarm the operating personnel when substantial surface defects appear, and moreover, to produce necessary inspection reports. An introduction of automatic inspection equipments like this has been based firstly on the fact that it is problematic to get manpower capable enough of doing this kind of work of a very monotonous nature, and secondly on the fact that an inspection carried out by a man is not at all possible any more when the strip speeds are increasing. The increased strip speeds and also the desire to provide an image as detailed as possible of the defects possibly occurring on the strip create a need to increase also the processing capacity of the automatic inspection equipment. The problem will then be the number of the operations needed. The fact is that if a 1500 mm broad strip moving at the speed of 300 m/min is inspected with the image dot size being 1 mm, the system shall be capable of analyzing 7.5 millions of image dots per second. In practice, it is possible to provide without excessive costs an equipment capable of doing 1.5 millions of image dot operations per second. However, such a speed requires already that relatively expensive equipments are used. If a further increase of the capacity of the equipment were desired, it would be necessary to acquire several equipments like this expensive as such and to place them adjacent to each other, each equipment arranged to inspect only a part of the strip width.